1. Field of the Invention
The present invention relates to an optical apparatus, such as a camera, which performs the drawing-out and drawing-in of an optical unit.
2. Description of Related Art
Heretofore, in zoom lens cameras capable of performing a zooming action, a cam ring is used as a means for driving a lens to perform the zooming action. A cam groove provided in the cam ring is formed, for example, in the shape as shown in FIG. 10(a). In FIG. 10(a), the cam groove 101 in the cam ring 100 is provided for driving a variator lens. A cam pin provided on a lens barrel holding the variator lens is fitted in the cam groove 101 and the lens barrel is arranged to move between a stowage position where the lens barrel is stowed within a camera body and a telephoto end position, according to the rotation of the cam ring 100. Incidentally, when the lens barrel is in the stowage position, a barrier (not shown) provided on the front end portion of the lens barrel is closed to protect the lens.
In the conventional zoom mechanism as described above, there is provided such a cam groove as to cause the variator lens to be drawn out monotonously (without being drawn in on its way) during the zooming action from the wide-angle side to the telephoto side and to be drawn in monotonously (without being drawn out on its way) during the zooming action from the telephoto side to the wide-angle side, and the lens barrel holding the variator lens is driven by a DC motor, serving as a zoom motor, and a train of gears so as to be moved in the optical axis direction.
In the meantime, there exists backlash in a train of gears. Specifically, when the lens barrel holding the variator lens is driven from the wide-angle side to the telephoto side, the backlash exists on the telephoto side. On the other hand, when the lens barrel holding the variator lens is driven from the telephoto side to the wide-angle side, the backlash exists on the wide-angle side.
In order to cause the lens barrel holding the variator lens to stop always at the same zoom position regardless of whether the zooming operation is performed by an operator from the telephoto side to the wide-angle side or from the wide-angle side to the telephoto side, it becomes necessary to perform a biasing operation for eliminating backlash.
A problem might arise in a case where the lens barrel is driven from the telephoto side, i.e., the position where the lens barrel protrudes from the camera body at the full length, to the wide-angle side, i.e., the position where the lens barrel is drawn within the camera body. In such a case, if the lens barrel happens to come into contact with an obstacle, or if the operator erroneously pushes in the lens barrel, exerting an external force on the lens barrel, the lens barrel would be pushed in as much as the backlash, so that the photo-taking magnification is caused to change.
In view of the above points of view, there has been proposed a camera in which, when zooming is effected from the telephoto side to the wide-angle side, a biasing operation, i.e., the operation of drawing in the lens barrel further by an extra amount from the position desired by the operator and, after that, drawing out the lens barrel, is performed to eliminate the backlash of a train of gears, so that the lens barrel can be stopped at the stop position desired by the operator, thereby solving the above conveniences.
On the other hand, there is another zoom mechanism in which, as shown in FIG. 10(b), an extreme value is set between the wide-angle end and the telephoto end in a cam groove 201 provided in a cam ring 200. In that zoom mechanism, when advancing from the wide-angle end to the telephoto end, the lens is moved toward the image side before reaching the extreme value, and is moved toward the object side after passing the extreme value.
In the above zoom mechanism, assuming that the zooming action is stopped between the wide-angle end and the extreme value during the process of zooming toward the telephoto end (herein, the rotating direction of a gear at this time is referred to as the normal rotating direction), the backlash occurring in a train of gears for driving the cam ring 200 is considered to exist on the side in the normal rotating direction. Then, since, in such a stop position, the direction in which the lens barrel advances toward the extreme value is the abovementioned normal rotating direction, if any external force is exerted on the lens barrel, the lens barrel would be drawn in, so that the photo-taking magnification is caused to change.
In order to remove such inconveniences, it is necessary to perform the biasing operation. However, since, in the conventional method, the biasing operation is performed only when the lens barrel is moved from the telephoto side to the wide-angle side, the biasing operation is not performed in a case where the lens barrel is moved from the wide-angle side to the telephoto side. Therefore, there is the possibility that, if the lens barrel happens to come into contact with an obstacle, or if the operator erroneously pushes in the lens barrel, exerting an external force on the lens barrel, the lens barrel would be pushed in slightly, so that the photo-taking magnification is caused to change.